Challenge

The Eau Claire, WI. facility’s secondary digester cover failed to provide adequate gas storage to allow use of the facility’s cogeneration facility for the five years since it had been installed.

The city requested Siemens Water Technologies remove and replace the existing ballasted fiberglass cover with a Dystor® membrane gas holder system. The solution also needed to provide 120 days of sludge storage due to the limited access to farmland for application of sludge during winter months.

Solution

Siemens installed a 100 ft. diameter Dystor membrane gas holder cover with support dome, an air supply system and electrical controls with gas detector.

• The operating pressure can be set at a pressure compatible with the structural capability of the existing covers.
• The Dystor cover allows plant personnel to vary the sludge level throughout the entire side-wall depth of the digester to meet the sludge storage requirements.
• The plant can now use the cogeneration system to produce electricity for use in the plant and to produce hot water for use in heating the primary digesters.

Results

Besides meeting the sludge storage requirements, the city of Eau Claire estimates that the installation of the Dystor membrane gas holder cover saves them up to $9,000 per month in electrical costs. This has resulted in a pay back period of about 3 ½ years.